FF baby with dark, dark green poo?

My LO was EBF up until 5 months, and in those 5 months, it was always a nice yellowish color. We started solids, so of course, his poo was the color of what he ate (carrots etc). Well, we have all had the flu the past few days so I have held off solids and doing just formula.. along with Tylenol and all the snot I am missing he is swallowing...

He pooed tonight and it was a DARK green? I mean, like almost black. Is this normal in FF babies? This is my first go-round with babies AND formula so.